1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a dual damascene interconnection with a metal-insulator-metal (MIM) capacitor and a method of fabricating the same.
2. Description of the Related Art
To improve the speed of semiconductor devices, there have been intensive studies on methods of reducing RC delays using low-resistance interconnections and low-k intermetal dielectrics (IMDs). Copper interconnections have a lower resistance than conventional aluminum interconnections and a relatively high resistance to electromigration, thus improving the reliability of semiconductor devices. Also, copper requires low power consumption and low price and thus has been widely used as interconnection material.
However, since copper is not easily etched, patterning a copper layer in a desired shape is very difficult. Thus, a damascene process is used. That is, after a groove is formed in an interconnection shape by patterning an IMD, copper is filled in the groove and then planarized using chemical mechanical polishing (CMP) to be on the same level with the IMD. In particular, a dual damascene process is widely used in which a via hole is formed and a line trench is formed over the via hole to overlap the via hole, and the via hole and the line trench are simultaneously filled with copper using a one-time deposition. By comparison, a via may be formed using a damascene process and then a line trench may be formed using another damascene process. In this case, the via and the line are each formed using a single damascene process.
Also, extensive studies have been made on metal-insulator-metal (MIM) capacitors, in which electrodes have no depletion and low-resistance metals are used, unlike conventional capacitors having an upper electrode and a lower electrode that are formed of polysilicon. However, when an MIM capacitor is formed in a conventional dual damascene interconnection, a dual damascene process has to be altered and the fabrication process becomes complex.
FIGS. 1 and 2 show conventional structures in which electrodes of an MIM capacitor are connected to interconnections using vias. To form these conventional structures, an MIM capacitor is formed before a via-level IMD is formed and an electrode of the MIM capacitor is connected to an interconnection by a via. However, in this case, as shown in FIGS. 1 and 2, a via that will be formed on the MIM capacitor and a via that will connect upper and lower interconnections are formed to different depths. As a result, a dual damascene process needs an etch process having a very high etch selectivity.
To form the structure shown in FIG. 1, a lower metal interconnection 4 and a lower electrode 6 of an MIM capacitor are formed using a copper damascene process on the same level in an insulating layer 2. A capacitor dielectric layer 8 is coated on the resultant structure, and then an upper electrode 10 and a capping layer 12 are sequentially formed. Next, an IMD 14 is formed, and then a via 16a connected to the lower metal interconnection 4, a via 18a connected to the lower electrode 6, and a via 20a connected to the upper electrode 10 are formed using a dual damascene process. Thereafter, upper metal interconnections 16b, 18b, and 20b are formed on the vias 16a, 18a, and 20a, respectively.
In the structure shown in FIG. 1, the types of available dielectric layers 8 are limited. The dielectric layer 8 should function as both a capacitor dielectric layer and a diffusion barrier layer to copper that is used to form the lower electrode 6. Thus, the dielectric layer 8 is actually a silicon nitride layer. Also, since the lower electrode 6 is polished using chemical mechanical polishing (CMP) during the dual damascene process, its surface morphology is degraded. Thus, the characteristics of the MIM capacitor depend on the integrity of an interface between the lower electrode 6 and the dielectric layer 8. Also, the copper constituting the lower electrode 6 diffuses into the dielectric layer 8. Most seriously, the vias 16a and 18a connecting the upper and lower interconnections are formed to a different depth from that of the via 20a formed on the MIM capacitor. Thus, an etch process having a very high etch selectivity is needed during the dual damascene process. To form the vias 16a and 18a separately from the via 20a because of the etch selectivity, an additional mask is required. Thus, the dual damascene process must be modified.
In FIG. 2, only a lower metal interconnection 24 is formed in the insulating layer 22 using a copper damascene process. A diffusion barrier layer 25 is formed on the insulating layer 22, and a lower electrode 26 of an MIM capacitor is formed using, for example, TaN. Then, a capacitor dielectric layer 28 and an upper electrode 30 are sequentially formed on the resultant structure. A capping layer 32 and an IMD 34 are formed on the upper electrode 30. Thereafter, a via 36a connected to the lower metal interconnection 24, a via 38a connected to the lower electrode 26, and a via 40a connected to the upper electrode 30 are formed using a dual damascene process, and upper metal interconnections 36b, 38b, and 40b are formed on the vias 36a, 38a, and 40a, respectively.
In the structure shown in FIG. 2, since the lower electrode 26 is not formed of copper, the types of material used in the dielectric layer 28 are more numerous compared to the structure of FIG. 1. Thus, the dielectric layer 28 can be formed of even high-k dielectric material. Nevertheless, in this structure, three different-type vias 36a, 38a, and 40a are formed requiring an etch process having a high etch selectivity or an additional photolithographic process. Therefore, the dual damascene process must be modified.
FIG. 3 shows another conventional structure in which an MIM capacitor is connected to an AlCu interconnection. In this structure, lower interconnections 42a and 42b are formed of AlCu, and then an insulating layer 44 is formed. Next, vias 46a, 46b, and 46c are formed of W using a single damascene process, and a lower electrode 48, a dielectric layer 50, and an upper electrode 52 are formed on the vias 46a and 46b to complete an MIM capacitor. Thus, the lower electrode 48 is connected to the lower interconnection 42a by the vias 46a and 46b. Next, a first IMD 54 is formed, an AlCu interconnection 55 is formed using a single damascene process, and a second IMD 56 is deposited thereon. Similarly, through a single damascene process, a W stud 58a connected to the upper electrode 52 and a W stud 58b connected to the AlCu interconnection 55 are formed in the second IMD 56.
In this case, unlike the cases described with reference to FIGS. 1 and 2, problems of an etch process due to different types of vias can be solved. However, since the single damascene process is performed several times, the copper dual damascene process must be somewhat modified. Also, while the MIM capacitor is being fabricated, the via 46c is exposed to an etching atmosphere, thus degrading the yield and reliability of the via 46c. To solve these problems, the vias 46a and 46b formed under the MIM capacitor and the via 46c connecting the upper and lower interconnections 42b and 55 should be formed using separate processes. However, this case necessitates an additional photolithography process.